Acute and long-term consequences of co-opted doublesex on the development of mimetic butterfly color patterns.

Novel phenotypes are increasingly recognized to have evolved by co-option of conserved genes into new developmental contexts, yet the process by which co-opted genes modify existing developmental programs remains obscure. Here we provide insight into this process by characterizing the role of co-opted doublesex in butterfly wing color pattern development. dsx is the master regulator of insect sex differentiation but has been co-opted to control the switch between discrete non-mimetic and mimetic patterns in Papilio alphenor and its relatives through the evolution of novel mimetic alleles. We found dynamic spatial and temporal expression pattern differences between mimetic and non-mimetic butterflies throughout wing development. A mimetic color pattern program is switched on by a pulse of dsx expression in early pupal development that causes acute and long-term differential gene expression, particularly in Wnt and Hedgehog signaling pathways. RNAi suggested opposing, novel roles for these pathways in mimetic pattern development. Importantly, Dsx co-option caused Engrailed, a primary target of Hedgehog signaling, to gain a novel expression domain early in pupal wing development that is propagated through mid-pupal development to specify novel mimetic patterns despite becoming decoupled from Dsx expression itself. Altogether, our findings provide multiple views into how co-opted genes can both cause and elicit changes to conserved networks and pathways to result in development of novel, adaptive phenotypes.